Planar inductor with operative calibrating in a RF system

Abstract: A thick-film planar inductor is made according to a specific geometry with conventional techniques. Such device is then operatively calibrated for tuning the circuit to which it is connected by changing the geometry of the inductor through laser etching.

Description: This invention relates to a planar inductor calibrated for obtaining the optimum value for tuning a radio frequency electronic circuit. Such callibrations allows the tuning to be carried out in a completely automatic way, the operative calibration being effected by changing the geometry of the planar inductor. The tuning of a RF electronic circuit is usually carried out by changing the value of the LC components of an oscillating circuit. In most cases the capacity is changed by means of varying capacitors. This involves the use of varying capacitors of relatively high cost as well as a tuning unstability in time. Moreover, in case a wire inductor is used, the tuning process consisting in a manual deformation of the inductor is a long, little precise operation. On the other hand thick-film planar coils as well as the method of calculating the size thereof are known at the state of art, however, such planar components are essentially fixed-value inductances and should have a varying capacitor connected in parallel for tuning the circuit. JP Patent A-4,148,514 relates to an inductance adjustment method by shaving off at least one part of a conductor pattern which forms a printed coil on a substrate. The inductance of the printed coil is set so as to be smaller than a prescribed value. While the inductance of the printed coil and the resonance frequency of a resonance circuit formed of the printed coil are being measured, one part of the conductor pattern is shaved off from its side part. When the prescribed value is obtained, the shaving operation is stopped. JP Patent A-4,094,505 relates to an inductance adjustment method by removing the edge of the conductor. Pattern which forms a printed coil on a substrate. The spiral-shaped conductor pattern comprises an inductance adjustment section, the adge of the latter is gradually removed by a laser beam or other means while measuring the inductance and reducing the area until the inductance reaches a specified value. The present invention seeks to provide a thick-film planar inductor which allows a RF calibration for the tuning to be fully automated. A further object of the present invention is to provide a serigraph planar inductor which cannot be deformed due to any mechanical stress occurring in the circuit. Still another object of the present invention consists in that the serigraph planar inductor is made by an apparatus operating according to the thick-film technology of standard use and limited cost in the frame of the present techniques of construction of the electronic circuits. The above-mentioned objects are achieved by a thick-film planar inductor formed by a serigraph sediment of conductive thick-film pastes, and through an operative automatic calibration which modifies the geometry of the inductor while tuning the circuit in which the inductor is connected. The geometry of the serigraph inductor and the value of the inductance is changed by varying the length of the path of the deposited conductive layer; said geometry of the serigraph inductor has suitable areas, the form of which can be changed by means of a kerf which can be made in the stripe of the conductive material, thus providing the extention of the inductor by separating two specific edges. In order to better explain the principles of this invention and the operation of the construction system of the inductor according to the invention without limiting the field of the possible applications thereof, an embodiment is shown in the accompanying drawings, in which: Fig. 1 is an enlarged view of the spiral used for the coil according to a preferred geometric configuration; Fig. 2 is a schematic block diagram of the instruments and interfaces of the apparatus for the construction of the inductor. With reference to Fig. 1 the rough geometry of the inductor is obtained by depositing a thick-film conductive paste of silver, platinum or gold by planar serigraphy on a ceramic substrate. This is accomplished by means of conventional known technologies. As can be seen in that figure, the geometry of the inductor, preferably a square spiral or fret, has suitable areas the form of which can be changed. Designated by A is the initial end of the inductance, by B the final end of the same, by C the kerf which can be made in the stripe of conductive material, thus providing the extension of the inductor by separating edges C' and C". After the planar construction is completed, the geometry of the serigraph inductor and then the value of the inductance is changed by varying the length of the path of the deposited conductive layer. To this end a YAG laser shown in Fig. 2 by block 2 is used, said laser etching the inductor at area C of Fig. 1. At the same time as the incision operation the electrical values 4 relative to the circuit to be tuned are evaluated by the schematic control system of Fig. 2 so as to carry out a calibration by a fine, automatic adjustment of the inductor. The electrical values 4 act on a laser controller 5 which controls the incision of the inductor. The frequency tuning is carried out by an amplitude calibration. When the resonant circuit (LC) is tuned to the frequency of the signal fed to its input by generator 1, the amplitude of the demodulated signal at the output is maximum. Software 6 controlling the incision of the planar inductor is designed to determine the maximum signal through the following sequence: etching the inductor until the output signal reaches a minimum threshold, such step serving to make the initial step of incision faster; etching the inductor (1 spot) until the output signal increases its amplitude, such detection is accomplished by block 3; completing the incision as soon as the amplitude of the signal is reduced. An important characteristic of mechanical non-deformability of the planar inductor is obtained in the RF circuits in which such operative calibration of the inductor is carried out with the result of a stability of the tuned frequency in time. The inductor provided by the present invention does not involve any step of manual assembling, can be interfaced to devices having components of different technology, and has the economical advantages of a low-cost technology such as the thick-film planar technology with short time of processing.

Claims: A thick-film planar inductor formed by a serigraph sediment of conductive thick-film pastes, and through an operative automatic calibration which modifies the geometry of the inductor while tuning the circuit in which the inductor is connected, characterized in that the geometry of the serigraph inductor and the value of the inductance is changed by varying the length of the path of the deposited conductive layer, having said geometry of the serigraph inductor suitable areas, the form of which can be changed by means of a kerf (C) which is made in the stripe of the conductive material, thus providing the extension of the inductor by separating two edges (C', C"). A thick-film planar inductor according to claim 1 characterized in that the geometry of the inductor is of the square spiral or fret type.

Inventors: LANZANO FRANCO, LANZANO, FRANCO
Applicants: TELECONTROLLI S P A, TELECONTROLLI S.P.A.
Application year: 1994
Main classification: H01F17
IPC codes: H01F17, H01F41